It is well known in the art that para-aramid polymers, such as those derived from terephthalic acid (T) and p-phenylenediamine (PPD) have a high modulus and relatively high tensile strength compared with conventional fibers. Such polymers are highly crystalline, and can be drawn very little, usually less than about 1%. Drawing and heat treating (annealing) of such polymers may result in large increases in modulus, but virtually no change in tensile strength. It is an objective of this invention to provide polymers which are relatively high in modulus, and drawable (much more than 1%), and whose tensile strength is greatly improved after drawing. Thus, selected substituted 4,4'-diaminobiphenyls (benzidines) are used to replace specific amounts of PPD in PPD/T polymers to form drawable aramids.
In another embodiment copolymers of 3,4'-diaminodiphenyl ether (herein sometimes referred to as ODA) and selected substituted 4,4'-diaminobiphenyls with terephthalic acid are also drawable aramids.
U.S. Pat. No. 3,349,062 mentions the possible use of 2,2'-dichloro-4,4'-diaminobiphenyl in aramids (at col. 6, line 58) but mentions no specific polymer incorporating this monomer.
In U.S. Pat. No. 4,785,038 a polymer reportedly derived from isophthalic acid and 2,2-dichloro-4,4'-diaminobiphenyl is made (Example 8).
In U.S. Pat. Nos. 4,384,107, 4,461,886 and 4,525,413 2,2'-dichloro-, 2,2'-dibromo- and 2,2'-dimethyl-4,4'-diaminobiphenyl are mentioned (in Examples 13, 17 and 15) as possible comonomers in aramids with various possible 4,4'-biphenyldicarboxylic acids. Also 2,2'-dibromo-4,4'-diaminobiphenyl is used in several examples in each patent to make aramids from biphenyl or stilbene containing diacids.
Japanese Patent Application 86/315,111 describes the aramids from 2,2'-dimethyl- and 2,2'-dichloro-4,4'-diaminobiphenyl, terephthalic acid, and 1,4-bis(4-aminophenoxy)benzene.
U. S. Pat. Nos. 4,075,172, 4,413,114 and 4,507,467 describe aramids prepared from ODA, units derived from terephthalic acid and other diamines. However, no mention is made of the use of substituted 4,4'-diaminobiphenyls. These aramids may be drawn up to about 1000%, but the resulting drawn polymers in form of a fiber, for instance, are amorphous.
European Patent Application 367,535 discloses aramids made from terephthalic acid, p-phenylenediamine, 3,4'-diaminodiphenyl ether, and substituted 4,4'-diaminobiphenyls with particular compositional ranges. For example, one polymer specifically disclosed is a copolymer of 2,2'-dimethyl-4,4'-diaminobiphenyl, terephthalic acid, 3,4'-diaminodiphenyl ether and terephthalic acid. The broadest compositional range disclosed in 367,535 for polymers containing first, second and third units (see below) overlap with the broadest compositional range claimed herein of polymers containing first, second and third units (see below). However, the range claimed herein does not overlap with the preferred range in 367,535, and no polymers claimed herein were actually made in 367,535. Furthermore, the inventors of 367,535 don't mention the drawability and excellent properties of the drawn polymers of the selected polymer compositions claimed herein.
In none of the above patents except EP 367,535 is a copolymer of 2,2'-dichloro-, 2,2'-dibromo- or 2,2'-dimethyl-4,4'-diaminobiphenyl with terephthalic acid, with or without units derived from PPD, specifically mentioned.
The drawing of polymers in general is well known to those skilled in the art, but the drawing of some aramids is more difficult. It is known to those skilled in the art that certain aramids that are essentially noncrystalline may be readily drawn. But crystalline aramids (such as PPD/T), which have the advantage of having relatively high tensile moduli and strengths are not readily drawable, that is they can normally be drawn only about 1-2% or less without substantial improvement of tensile strength. Higher amounts of draw would be expected to lead to still better alignment of the polymer chains and hence higher tensile strengths. Thus, it would be desirable to be able to draw aramids, as in the fiber form, such that the "highly" drawn aramid would have improved tensile strength and have substantial crystallinity.
U.S. Pat. No. 3,869,430 describes the drawing of PPD/T fibers, and says they can be drawn up to about 3%. However, in the only example in which they are drawn, they are reported drawn from 0.1 to 2.1%.
Example 1 of U.S. Pat. No. 3,869,429 describes the drawing of a PPD/T fiber 0.5%.
U.S. Pat. No. 4,500,278 describes the drawing of PPD/T fibers, and discloses that it is possible to draw the fibers up to 1.6%.
Japanese Patent Application 63/006108 discloses the drawing of PPD/T fiber greater than 2%. However this fiber contains more than 50% water.